Self-centering arrangement for grinding the hardmetal pins of drill bits

ABSTRACT

An arrangement for grinding the hardmetal pins of drill bits, e.g. the tungsten carbide buttons (31) of button bits (1), comprises means (parallel arms pairs 9 and 10) for adjusting the position of a grinding pin (15) in relation to the drill bit (1) and also journalling means (4) operative to cause the grinding machine (3) to move relatively slowly in a circuit path around the button on the drill bit (1) to be ground and to cause the grinding pin (15) to rotate rapidly around its longitudinal axis. The drill bit is clamped securely in a stationary holder arrangement (2) which includes a tiltable table (35) which can be adjusted to and locked in selected angular positions.

TECHNICAL FIELD

The present invention relates to a self-centering grinding arrangementfor grinding the hardmetal pins or working tips of drill bits and morespecifically, but not exclusively, for grinding the tungsten carbidebuttons of button bits of the kind used, e.g., for drilling wells orlike down-the-hole drilling operations in the mining industry. Thearrangement includes a stationary holder arrangement in which the drillbits are clamped and which accommodates a liquid-coolant collectingvessel. The arrangement also includes a grinding machine equipped with agrinding pin which rotates about its longitudinal axis, and a grindingmachine journalling device which extends at an angle to the longitudinalaxis of said pin. The journalling device functions to impart rotarymotion to the grinder, with the center of rotation lying in the centerof the grinding pin.

BACKGROUND ART

Examples of self-centering grinding arrangements intended for grindingthe tungsten carbide buttons of button bits of the aforesaid kind aredescribed in Swedish Patent Application No. 8604159-7. The grinding pinof these known grinders executes two distinct forms of movement, i.e.the pin rotates about its own longitudinal axis and also carries out asuperposed circuitous or orbital movement. The grinding machine and itsdrive means are mounted on a column-carried jib arm which can be raisedand lowered, up and down the column. The bit to be ground is clamped ina fixture or jig which can be moved freely on an electromagnetic table,when the table is not magnetic. Initially, the fixture in which the bitis clamped is brought into approximate alignment with the grindingmachine, whereafter the jib arm is lowered, so as to bring the grindingpin into engagement with the carbide button of the bit to be ground.Since, at this stage, the fixture is able to move freely on the table,it is said that the carbide button will center itself in relation to thegrinding pin. Subsequent hereto, the table is brought to its magneticstate, such as to lock the fixture in position on the table.

This known grinding arrangement thus includes a holder arrangement whichcan be moved in the horizontal plane. A similar grinding arrangement isdescribed and illustrated in Swedish Patent Application No. 8702950-0,in which the bit holder arrangement includes a carriage which runs on aplatform and which can be raised and lowered relative to the grindingmachine. The grinding machine is attached to the top of a stand or frameand is mounted for limited vertical movement therein.

Such known grinding arrangements, however, do not permit bits to beground in a rational manner, since only one bit can be clamped in theholder at any one time. It is also doubtful that effectiveself-centering of the button actually takes place, since the holder andthe load carried thereby, i.e. the bit, constitute a heavy andrelatively sluggish unit which has to be acted upon by the grinding pinitself, in order to center on the pin. Another problem which is notsolved satisfactorily by the known grinders is one of controlling theforce at which the grinding pin is intended to bear against eachindividual button on the bit. In the case of known grinderconstructions, it would appear that this problem is solved through theintermediary of the weight exerted by the grinding machine and itsjournalling devices.

SUMMARY OF THE INVENTION

All of the aforesaid problems are solved by the inventive self-centeringgrinding arrangement, in that the grinding machine journalling device ismoveable both horizontally and vertically in relation to the bit holder,which is stationarily mounted. The grinding machine journalling deviceis carried on pairs of mutually parallel arms which are journalled forrotation on a vertically extending stand or frame structure and whichco-act with pneumatic piston-cylinder devices. The cylinder infeedpressure can be switched to a grinding pressure mode, in which grindingpressure acts vertically during a grinding operation, and acompensating, auxiliary pressure mode for facilitating manual movementof the grinding machine.

The inventive grinding arrangement enables the grinding pin setting tobe readily adjusted manually, due to the fact that the weight of thegrinding machine is counteracted by the compensating functions of thepiston-cylinder devices, i.e. the aforesaid auxiliary pressure mode. Aself-centering effect, or fine adjustment of the grinding pin setting,is achieved automatically, by switching the cylinder input pressure tothe grinding pressure mode. Due to the full freedom of movement of theinventive grinding machine journalling device in all space planes, it ispossible to grind a multiple of drill bits in a rational manner. Forinstance, the stationary bit holder arrangement can be provided with twobit holders for a corresponding number of bits. The grinding machinejournalling device can be swung to a position in which it is locatedabove respective holders, or above a drill bit which, because of itsdimensions, has been located outside the holder arrangement, and thecylinder input pressure then switched to its grinding pressure mode.

The holders provided in the holder arrangement preferably have the formof recesses located in at least one tiltable table which is capable ofbeing stopped and locked in desired angular positions and which hasmounted beneath its upper surface, i.e. the table top, a pneumaticallyoperated piston rod for each holder. A well-defined location of thedrill bit in respective holders can be achieved by providing each recesswith a corner piece and by directing piston movement towards said cornerpiece, the stem of the bit being inserted into the recess and clampedagainst the corner piece by means of the activated piston rod. In orderto enable drill bits of widely varying dimensions to be held firmly inrespective bit holders, the tiltable table is provided with a bottomplate which can be displaced positionally beneath the recess, such as toallow smaller drill bits having relatively short stems to rest againstthe plate.

Although two separate tiltable tables, each provided with two drill-bitholders, can be served by one and the same journalling device, anadvantageous and preferred embodiment is one in which each table isprovided with an individual journalling device and therewith with anindividual grinding machine. This embodiment greatly rationalises thehandling of drill bits to be ground, since two bits can be groundsimultaneously, while the operator is able to remove a ground bit fromone table and insert in the adjacent holder a fresh bit to be ground, inrespective tables.

The holder arrangement and associated collecting vessel are constructedso as to function as a transport container for transportation of thegrinding arrangement in its dismantled state, the grinding arrangementcomponents being accommodated in the transport container.

DESCRIPTION OF PREFERRED EMBODIMENTS

The self-centering grinding arrangement according to the presentinvention will now be described in more detail with reference to apreferred embodiment thereof and with reference to the accompanyingdrawings, in which

FIG. 1 is a side view illustrating the principle construction of aninventive grinding arrangement;

FIG. 2 is a sectional view of the journalling device operative inimparting orbital movement to the grinding machine;

FIGS. 3a-b illustrate a preferred embodiment of the inventive grindingarrangement; and

FIG. 4 is a perspective view of a preferred embodiment of a multi-bitholder arrangement.

FIG. 1 illustrates the principle construction of a grinding arrangementaccording to the present invention. The grinding arrangement comprises abit holding arrangement for those bits whose tungsten carbide buttons 31are to be ground. The arrangement also includes a journalling device 4which is intended to carry a grinding machine 3. The grinding machine 3includes a drive motor which rotates a grinding pin 15 at high speedabout its longitudinal axis. The journalling device also includes afurther drive motor which has a shaft 24 on which the grinding machine 3can be adjustably mounted, by means of an attachment means 25. The drivemotor of the journalling device 4 is operative to impart circuitous ororbital movement to the grinding machine 3 and its grinding pin 15, withthe center of rotation in the grinding center 30 of the grinding pin 15(FIG. 2).

The journalling device is carried by parallel arm pairs 5, 7 which arejournalled on a post or column 6 for rotation through an angle of 360°.The post 6 is mounted on a floor frame 17.

Each of the parallel arm pairs 5, 7 includes an inner and an outer armpair 9 and 10 respectively, such that the journalling device 4 and thegrinding machine carried thereby can be moved freely, both verticallyand horizontally, within the span of the parallel arm pairs 5, 7. Thegrinding pin 15 is brought manually into alignment with the tungstencarbide button to be ground, by gripping a handle 8 and moving thegrinding pin 15 to a position immediately above the button 31. Thismanual movement is facilitated by a double-acting, pneumaticcompensating piston-cylinder device 11, 12 provided between the pivotalarms within respective arm pairs 9, 10. When pressure is fed to thepneumatic piston-cylinder-devices 11, 12, the pistons exert acompensating force on the parallel arm pairs 5, 7, such that thejournalling device 4 will remain stationary in the position to which itwas adjusted manually by the operator. An adjustable pressure regulator13 is included in the supply circuits of respective piston-cylinderdevices 11, 12, for the purpose of achieving a correct balancing effect.

The supply circuits of the piston-cylinder-devices also include a switch14 which is operative to switch the direction of air supply, such as tocause the parallel arm pairs 5, 7 to exert a vertical downward force onthe journalling device 4 and the grinding machine 3. This facility isutilised for the automatic, continuous grinding operation describedherebelow.

FIG. 2 illustrates the principle construction of the journalling device4. The main components of this device include a housing 22, which housesthe further drive motor 23 and its output shaft 24. The drive motor issupplied with air under pressure from the same conduit as that used tosupply air under pressure to the grinding machine 3. Arranged in thebranch leading to the drive motor 23 is a throttle valve 26, by means ofwhich the operator can regulate the flow of air to the further drivemotor 23 and control the speed of said motor from zero to maximumvalues.

The output shaft 24 is journalled in the housing 22 on two ball bearings27 and has provided therein three passageways which are supplied withair to and from the grinding machine 3 and with cooling water to saidmachine, via a swivel switch 28. The passageways are connected to thegrinding machine 3 by hoses 29.

The grinding machine attachment 25 is attached to the lower end of theoutput shaft 24 at a given angle which is so adapted that the grindingcenter 30 of the grinding pin 15 will coincide with the rotational axisof the output shaft 24, despite the fact that the grinding machine isangularly positioned. As a result hereof, the drive motor 23 will drivethe grinding machine 3 in a circuit path during a grinding operation,therewith providing a highly satisfactory grinding result. As mentionedabove with reference to FIG. 1, the attachment 25 can be adjusted tomutually different angular positions for adaptation to the angularposition of the drill bit to be ground.

FIGS. 3a and 3b illustrate a preferred embodiment of the inventivegrinding arrangement. The arrangement is shown in side view in FIG. 3aand in front view in FIG. 3b. The majority of the reference numeralsused in FIGS. 3a and 3b are found in FIG. 1 and identify mutuallycorresponding components of the two embodiments.

In the case of the illustrated and described preferred embodiments, thejournalling device 4 suspended from the parallel arm pairs 5, 7 includessupply devices for air supply A, B and cooling water supply C, each saidsupply device being connected, via the swivel switch or coupling, to thegrinding machine by a respective pivotal pipe A', B', C', these pipescorresponding to the hoses 29 of the FIG. 1 embodiment. The conduit Aincorporates the throttle valve 26 referred to with reference to FIG. 2.

FIGS. 3a and 3b ilustrate more clearly the preferred embodiment of theadjustable attachment means 25. This attachment means includes a casingwhich has formed therein two arcuate grooves or channels for coactionwith locking pins and locking devices 33 associated therewith, therebyenabling the position of the grinding machine to be fixated relative tothe journalling device 4. The angle subtended between the longitudinalaxis of the grinding pin 15 and the longitudinal axis of the drive shaft24 can therefore be controlled, which is desirable for effective controlof the amplitude of the orbital or circuitous movement before mentioned.

FIG. 4 illustrates a preferred embodiment of a drill-bit holderarrangement 2 intended for holding the drill bits whose tungsten carbidebuttons 31 are to be ground. The holder arrangement comprises a box 18having an upwardly facing opening 34 in which one or more tables 35 arepivotably mounted, as indicated by the axle 20 and the arrow 21 inFIG. 1. Each table 35 includes two or more holders 19 in the form ofsubstantially rectangular recesses, into which the stem of the drill bit1 is inserted. The holder 19 also includes a pneumatic piston-cylinderdevice whose piston 36 functions to hold the drill bit 1 lockedeffectively against the walls of said recesses. The piston-cylinderdevice of respective holders 19 is preferably arranged such that thepiston of each said device will operate in the direction of one diagonalof the recesses, therewith to lock the drill bit 1 effectively againstone corner of the recesses, as will be seen from the table 35 shown tothe left in FIG. 4.

The piston-cylinder devices of the holders 19 are operated by means of avalve 37, which is housed in a casing 38 in order to shield the valveagainst unintentional activation. Consequently, the operator can onlyactivate the valve 37 from the mutually opposite open sides. Whenactivated from one side, the valve 37 will operate to impart lockingmovement to the piston cylinder-device, and when activated from theother side will impart a release movement to said device.

As will be seen from FIG. 4, the holder 19 is provided with adisplaceable floor 39, which enables the holder to accommodate drills ofsmall dimensions in a ready manner. The floor 39 is displaced with theaid of a lever 40. In the FIG. 4 illustration, the floor 39 of theleft-hand table 35 is shown to be displaced to a position in which itwill support drill bits 1 of small dimensions. The floor 39 of theright-hand table of the illustration has been moved away, so as toenable drill bits 1 of large dimensions to be fitted, the head diametersof these bits being so large as to allow the heads to rest on thesurface of the floor 39, when the drill stem is inserted into one of theholder recessess of the table.

As mentioned above, each table can be adjusted to a desired angularposition. This adjustment is facilitated by means of a lever 41, whichcan be pulled or drawn up in the manner shown at the right-hand table inFIG. 4. The table can be locked in its selected position, by means of alocking device 42.

The box 18 serves as a collecting vessel for the liquid coolantdelivered to the grinding location from the grinding machine during agrinding process. Detachable splash guards 43, of which only one isshown in FIG. 4, can be fitted to all side walls of the box 18. The box18 is connected to a circulation pump and filter arrangement, forrecycling the liquid coolant to the grinding machine 3.

A further advantage afforded by the box 18 is that the box is adapted toaccommodate the whole of the grinding arrangement. Subsequent to beingdismantled to a given extent, the grinding arrangement can be packedinto the box 18, which then serves as a transportation crate. It isindicated in FIG. 4 that the illustrated preferred embodiment of theholder arrangement 2, comprising two tables 35 which can be manouveredindependently of one another, can be assigned two grinding machines 3,each journalled in parallel arm pairs 5, 7. This enables drill bits ofmutually different dimensions to be ground separately at one and thesame time. By providing each table with two holders 19, the possibilityis afforded of switching bits in one of the holders while grinding a bitin the other.

Naturally, it lies within the purview of the invention to fit the box 18with only one tiltable table 35 and also to use only one grindingmachine 3 with each box 18.

When the inventive grinding arrangement is to be brought into use and istransported to its place of use in the box or crate 18, the variouscomponents are removed from the box and assembled together, whereafterliquid coolant is introduced into the grinding arrangement and thearrangement is connected to suitable compressed air sources. Thegrinding arrangement is now ready for use.

The drill bits 1 whose tungsten carbide buttons 31 are to be ground areclamped in respective holders 19 on the tables 35. The tables are theninclined to positions for grinding the buttons located on the crown orperiphery of respective bits. The grinding pin 15 of the grindingmachine 3 is then moved forwards to the first button 31 to be ground.During this adjusting movement of the grinding pin 15, compressed air issupplied to the compensating piston-cylinder devices 11, 12 of theparallel arm pairs 5, 7, so as to enable the operator to bring thegrinding pin 15 manually into position, centrally above the button 31,in a ready and easy fashion. Subsequent to bringing the grinding pininto alignment with the button 31, the operator manipulates the switch14, so as to switch the supply of compressed air from the compensatingpiston-cylinder devices 11, 12 to the grinding pressure facility, whilestarting the drive motors 3 and 23 at the same time. The grinding pin 15will automatically find its correct grinding position on the tungstencarbide button 31, through a self-centering action, and grinding iscommenced.

As the drill bit is being ground, the operator is able to exchangeground bits for fresh, worn bits in a holder located adjacent the holdercontaining the bit being ground. Subsequent hereto, there remainsnothing else for the operator to do, other than to switch off thegrinding arrangement when grinding of said bit is completed. Uponcompletion of this working operation, the switch 14 is turned to itscompensating position and the grinding pin 15 is moved manually to afresh button to be ground. The aforesaid automatic self-centering actionand subsequent grinding procedure are then repeated.

When the drill bits to be ground have large dimensions, such that thedrill stems are too large for the holders 19, the parallel arm pairs canbe rotated on the post 6 to a position externally of the box 18. Thedrill bits of excessively large dimensions can be clamped in thisposition with the aid of suitable means and the tungsten carbide buttonsthereof ground with the aid of the same machine used to grind the drillbits of smaller dimensions.

In those instances when the button of a drill bit to be ground isexcessively worn and it is consequently necessary to grind down materiallocated around the button, there is used a grinding pin which isparticularly intended for this purpose. This particular grinding pinrequires the grinding machine to be held firm in one and the sameposition. Such locking of the grinding machine can be achieved readilywith the inventive construction, by closing the throttle valve 26 andtherewith stopping rotation of the rotating journalling device 4.

All types of rock drilling equipment, i.e. drills of different profilesand different sizes, etc., can be ground with the aid of the inventivegrinding machine, and the invention is not therefore restricted tobutton bits provided with tungsten carbide buttons.

It will also be understood that the invention is not limited to thedescribed and illustrated embodiments thereof and that modifications andchanges are possible within the scope of the following claims. Forexample, the drill bit holder can be configured in a manner which willtailor the holder to a drill bit of particular manufacture. Furthermore,the arrangement may include a pump system operative to pump liquidcoolant from the collecting vessel 18 back to the grinding machine 3.

We claim:
 1. A self-centering arrangement for grinding the hardmetalpins of drill bits of the kind used within the mining industry fordrilling wells and like down-the-hole drilling operations, in which thedrill bits (1) are clamped in a holder arrangement (2) including aliquid coolant collecting vessel (18) and which grinding arrangementincludes a grinding machine (3) equipped with a grinding pin (15) drivenby motor (23 to rotate about its longitudinal axis and further includesa grinding machine journalling device (4) which is positioned at anangle to the longitudinal axis of said grinding pin (15) and which isoperative to allow the grinding machine (3) to move in an orbital pathwith the center of rotation lying in the grinding center of the grindingpin (15), characterized in that the grinding machine journalling device(4) is moveable in the horizontal and the vertical plane relative to theholder arrangement (2), which is stationary; and in that the journallingdevice is mounted on parallel arm pairs (5, 7) pivotally mounted on avertical stand (6) said parallel arm pairs (5, 7) comprise an inner andan outer arm pair (9 and 10 respectively) which are pivotally connectedtogether; in that the arm pairs (9, 10) coact with a piston-cylinderdevice (11, 12) acting on one pivot arm of said arm pair; in that theinner arm pair (9) is carried by the vertical stand (6) and the outerarm pair (10) is carried by the grinding machine journalling device (4);and in that the route of the supply pressure to thepiston-cylinder-devices can be switched by means of a valve switch (14)to provide a vertically acting grinding pressure during an automaticgrinding operation and to provide a compensating auxiliary pressureduring normal manual movement of the grinding machine.
 2. An arrangementaccording to claim 1, characterised in that the stationary holderarrangement (2) includes at least one tiltable table (35) having atleast two holders (19) for a corresponding number of drill bits (1); inthat the said at least one tiltable table (35) can be locked in adesired angular position for grinding both axially directed tungstencarbide buttons (31) on the drill bit (1) and buttons which are directedat an angle to the axis of said bit.
 3. An arrangement according toclaim 2, characterised in that the stationary holder arrangement (2)includes two separate tiltable tables (35) each of which includes twoholders (19); and in that each table is assigned one journalling device(4) and an associated grinding machine (3).
 4. An arrangement accordingto claim 1, characterised in that the grinding machine journallingdevice (4) includes a housing which is mounted on the free end of theouter arm pair (10) of said parallel arm pairs and which houses a drivemotor (23) for effecting said orbital movement, said motor (23) having ashaft direction which, by means of the parallel arm pairs (5, 7), isheld parallel with the vertical stand (6) carrying the inner arm pair(9) of said parallel arm pairs, and in that the grinding machine isattached to the shaft (24) of the drive motor by means of an attachment(25) which can be locked in mutually different positions, therewithobtaining said angular position between the longitudinal axis of thegrinding pin (15) and the grinding machine journalling device (4).
 5. Anarrangement according to claim 4, characterised in that the attachment(25) includes a casing in which there is formed at least one arcuategroove (32) in which a locking pin (33) extending from the grindingmachine (3) protrudes such as to fixate the grinding machine in adesired angular position relative to the shaft (24) of the drive motor.6. An arrangement according to claim 5, characterised in that each ofthe holders (19) of the table (35) has the form of a recess provided inthe table top and fitted with a corner piece against which the stem of adrill bit (1) inserted in the recess is held clamped by means of apiston-cylinder-device (36) located beneath the top of the table (35).7. An arrangement according to claim 6, characterised in that eachrecess (12) in the table top has an area sufficiently large toaccommodate drill bits (1) of a broad dimensional range; and in that thetable (35) has mounted therein a bottom plate (39) which can bedisplaced in said recess and which functions to support the short stemsof drill bits (1) of smaller dimensions.
 8. An arrangement according toclaim 4, characterised in that the drive motor shaft (24) is configuredwith a plurality of passageways intended for supplying air and coolingliquid to hoses (A, B, C) provided on the grinding machine, via swivelcouplings (28).
 9. An arrangement according to claim 2, characterised inthat the vertical stand includes a tubular post on which the inner armpair (9) is mounted for pivotal movement in a horizontal direction; andin that the outer arm pair can be moved manually between different drillbits (1) in the stationary drill bit holder arrangement (2) and also todrill bits clamped outside the stationary holder arrangement.